I'm working on my first project: a garage door opener that can be triggered by RFID or fingerprint. The existing opener hard-wired button has multiple functions, but works by sending different voltages to the opener. After checking with the manufaturer, I found that a momentary switch alone (or just closing the circuit) would open/close the door but I'd lose the other functions, which was fine. So I have the Nano triggering a relay (wired NC) when a valid RFID or fingerprint is scanned. he project concept works, but I don't have a convenient power source. The wiring for the original button runs on 24v, but closing the circuit to trigger the door open/close actually cuts off the 24v. I had planned on using the 24v with a buck converter in series with the 24v, but if closing the circuit brings voltage to 0, the Nano will turn off. So now I'm trying to power the Nano via a 9v battery but only when the relay opens. So I'm thinking of using a LTC4412 PowerPath to automatically switch to the 9v for a second just to keep it running, then back when the relay closes the circuit and 24v are restored. This should work, but I have no idea how to pick the right p-channel MOSFET for this. Any help would be appreciated.
I am planning a similar setup, especially since I have Alexa Auto in my car. "Alexa, open the pod bay doors, please".
Do the same way that a Ring doorbell works. Charge a supercap that acts like a UPS for the brief moment the switch is closed.
Start with this: 24VAC/5VDC converter.
That 24V is coming through a pullup resistor, you can't use it to power anything. Putting any kind of load on it could look like a button press to the door opener.
Pulled the circuit board on the button and you're right. One resistor, with the button closing the circuit. Back to the drawing board. Thanks.
You need a power supply. Batteries are useless for this.
The most convenient and inexpensive is usually a USB "phone charger" - almost all are rated at least 1 Amp at 5 V.
As the Raspberry Pi is isolated from the garage door circuit, you could configure a circuit made up from a transistor & relay to operate, depending on the voltage across the door switch – then monitor the relay volt-free contacts via the Raspberry Pi.
You could then similarly use a relay to operate the garage door switch, powered/controlled by the Raspberry Pi.